[PATCH 1/2] xen/irq: Cleanup the find_unbound_irq

Konrad Rzeszutek Wilk
2010-12-09T21:00:26Z

The "find_unbound_irq" is a bit unusual - it allocates
virtual IRQ (event channels) in reverse order. This means
starting at the "top" of the available IRQs (nr_irqs) down
to the GSI/MSI IRQs (nr_irqs_gsi).

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
drivers/xen/events.c | 18 ++++++++++++------
1 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 31af0ac..4d4a23d 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -405,15 +405,21 @@ static int find_unbound_irq(void)
{
struct irq_data *data;
int irq, res;
- int start = get_nr_hw_irqs();
+ int bottom = get_nr_hw_irqs();
+ int top = nr_irqs-1;

- if (start == nr_irqs)
+ if (bottom == nr_irqs)
goto no_irqs;

- /* nr_irqs is a magic value. Must not use it.*/
- for (irq = nr_irqs-1; irq > start; irq--) {
+ /* This loop starts from the top of IRQ space and goes down.
+ * We need this b/c if we have a PCI device in a Xen PV guest
+ * we do not have an IO-APIC (though the backend might have them)
+ * mapped in. To not have a collision of physical IRQs with the Xen
+ * event channels start at the top of the IRQ space for virtual IRQs.
+ */
+ for (irq = top; irq > bottom; irq--) {
data = irq_get_irq_data(irq);
- /* only 0->15 have init'd desc; handle irq > 16 */
+ /* only 15->0 have init'd desc; handle irq > 16 */
if (!data)
break;
if (data->chip == &no_irq_chip)
@@ -424,7 +430,7 @@ static int find_unbound_irq(void)
return irq;
}

- if (irq == start)
+ if (irq == bottom)
goto no_irqs;

res = irq_alloc_desc_at(irq, -1);
--
1.7.1